Darth_V8r

iTrader: (4)

aftermarket. my heads are aftermarket

G Atsma

Got it! Thanks man! (Filed for future use.....)

GaragebuiltSS

iTrader: (1)

.080 chromoly tsp pushrods, think those could be flexing?

And I did not check PTV.

hammertime

iTrader: (1)

I know you don't want it to be loss of valve control, but other than swap heads, you may not have done anything to address the problem. You should be able to CC the head reasonably close to get some idea what size the chambers are. That might give you some indication if too much has been milled off the heads.

Aside from that, what is the installed height of your springs versus your lift and what the manufacturer recommends? Dual springs that aren't properly installed are worse than a beehive with the correct rate and install height.

What cam and lifters are you running? What is the actual installed Intake Centerline? How large are the valves in the Pro Comp heads? Is this in a manual transmission car that might have experienced a mechanical over-rev?

Also, if you swapped excessively milled heads with thin gaskets for some stock unmolested 241's with MLS gaskets, you probably gained 0.030" to 0.040" PTV clearance, maybe even more, but your pushrods may be too short now if you have short travel lifters.

The devil is in the details - hope you get it sorted out.

GaragebuiltSS

iTrader: (1)

1. I will find the installed height
2. Ms3 cam 238/242 .600/.600 and ls7 lifters
3. I don't know the intake centerline
4. 2.02/1.65
5. It is a m6 car but I haven't over revved it that I know of.

KCS

iTrader: (20)

I'm having a hard time imagining how that could happen. How does that work exactly?

Darth_V8r

iTrader: (4)

Depending on spring rate possible. if your springs are 380 lbs open, you are probably OK. if they're 425+ open, then could definitely have contributed.

GaragebuiltSS

iTrader: (1)

Can someone explain the spring pressure thing? You're saying it should be 380lbs with the valve open? Why would it be bad for it to be higher like you said?Edit: just looked on comps site and the springs I have are 448lb open

G Atsma

Too high and you risk bending pushrods of the spec(.080 x 5/16") you mention.

MuhThugga

Valve float?

KCS

iTrader: (20)

How it causes pistons to hit intake valves.

GaragebuiltSS

iTrader: (1)

so I should go to a lighter spring? How would a heavier spring cause the valve to hit the piston?

Darth_V8r

iTrader: (4)

I'll try to explain it. I struggle sometimes with this, so please bear with me.

The pushrod actually has to move quite a lot of load. The rocker ratio is such that the spriong load is multiplied by 1.7x. Also, the valve area times the cylinder pressure. On the exhaust valve, the cylinder pressure is a much higher portion of the load as compared with the intake valve.

Think of pushing against a brick wall with a paper clip. After a certain amount of force, the paperclip will buckle. now move up to a coat hanger. it will still buckle, but it will take more force before it buckles under the load.

Now, consider the valve and spring assembly as the brick wall. A pushrod that is too thin or weak, it will flex under load. It can happen under two conditions. Once you clear the lobe and the lifter is on its way back down, the pushrod will snap straight. This has the effect of momentarily pole-vaulting the valve. This tends to be well away from TDC and tends to eat up the cam lobe. Secondly on the initial valve lift, it flex and then spring stright, throwing the valve "off" the lobe momentarily and into the piston. In particular, this will happen with the intake valve, because it opens near TDC.

If you have two pushrods at 5/16" - one with .080 thick walls and one with 0.105 thick walls, you will gain around 20% strength / stiffness. if you move to 11/32" diameter pushrods, you gain approx. 70% IIRC stiffness. And I think we can all agree when it comes to rods, stiffer is always better.

So, if you increase spring rate from 380 to 450 lbs, the actual increased load on the pushrod is from 648 lbs to 760 lbs. And that's before you have to account for cylinder pressure compensation, etc. So there are two corrective actions available for you:

1. Go to a thicker pushrod to prevent the flexion
2. Go to a lower spring rate, such as BTR dual platinums

Either option or both are beneficial. up to .625 lift, 380 lbs is plenty. FWIW, I run the AFR 8019 springs and 11/32 x .105 pushrods, and have zero valve control issues. my PTV is only 0.080. Been running this for over a year now DD.

I hope that explanation works for you. if not, i did my best, but someone else on here can rpobably make it make more sense.

G Atsma

Well, I sure got educated here! Thanks Darth!

KCS

iTrader: (20)

I find that part really hard to believe. I really don't think the pushrod can flex and spring back fast enough to loft the valve while it's still close enough to hit the piston.

Typically valve float looks like this, where the valve lofts near lax lift, at which point the piston is closer to BDC. Then there's the valve bounce at the closing point, but the piston is still more than halfway down the cylinder.

hammertime

iTrader: (1)

Let me first state that I am well aware TSP no longer uses Comp XE-R lobes. Since they have proprietary lobes the actual specs are a mystery, but one could infer that they are perhaps similar to the XE-R for sake of discussion.

Having said that, if you look at the Comp Master Lobe Catalog, the Extreme Energy XE-R lobe #3729 with 238 degrees of duration at 0.050 lift shows the tappet lift at TDC is 0.079" when installed on a 110 degree Intake Center Line, and 0.095" installed on a 106 degree ICL. Factor in your rocker ratio (multiply those figures by 1.7 respectively) and the valve is 0.134" off the seat on the 110 ICL, 0.162" off the seat at on the 106 ICL.

Without knowing your ICL or having measured the Piston to Valve clearance on install, its hard to say how close you were(are?) to making contact. That cam is one of TSP's largest that is designed to fit in a stock LS1 with unmilled heads and MLS gaskets. With all the unknowns here, and considering the larger valves, you are really fortunate the damage was not worse.

Darth_V8r

iTrader: (4)

Thanks for setting me straight

GaragebuiltSS

iTrader: (1)

that makes sense. I pulled those heads off and put on a set of untouched 241's everything else being the same and I'm fairly certain that aren't hitting now. I'm gonna pull the plugs out since it has been ran and check the pistons with a bore scope, if it hasn't hit with the new heads on then the others have to be milled. Thanks for all the info.

truckdoug

iTrader: (25)

thats a pretty long duration cam. you can get into trouble as the piston is chasing the intake valve closed. check PTV with some clay before you final torque them down.

hammertime

iTrader: (1)

truckdoug if you read my post above, you can see that Comp posts TDC clearance values based on intake centerline. That's TDC between the exhaust valve closing (end of exhaust event) and intake valve opening (beginning of intake event). While you are correct that the intake valve is closing while the piston is coming back up (starting the compression event) it should not be anywhere near the open intake valves, else there would not be any compression.

Since the OP does not know where the cam is installed, we don't know if it is too advanced. In the example above, four degrees advance translated to 0.028 less clearance. I whole heartedly agree that measuring PTV clearance with clay or with a dial indicator and checking springs would be highly recommended with a cam of this duration.